Cellular ink transfer rollers, for example anilox rollers, usually have a base body, for example of steel, which may be supplied with shaft extensions for holding the roller in suitable bearings, coupling to drive wheels or gears, or the like. The steel body may have the cells or depressions engraved therein; it is customary, however, to apply a layer of engravable material on the steel body and to form the depressions therein, leaving ribs or ridges or webs projecting from the walls of the cells between the cells themselves, which may be of wear-resistant material. Ink is supplied to anilox rollers frequently from chambered ink supply units, supplied at an upper and a lower side of the chamber with doctor blades, which wipe and rub against the outer surface of the thus formed cellular roller. The referenced U.S. Pat. No. 5,191,703, John, based on U.S. Ser. 07/762,582, filed Sep. 19, 1991 describes a roller in which hard ridges or ribs of chromium dioxide, aluminum oxide ceramic or the like, form the outer surface region of the anilox roller. The cells themselves are formed in a softer material between the ribs, for example copper.
The quantity of ink which can be accepted by the cells depends greatly on the depth of the cells, that is, the depth dimension from the outermost surface of the anilox roller. This dimension which is normally determined by the projection of the ribs or ridges above the lowermost point of the cells. A common concept is the ink transfer number. This ink transfer number is defined as the quantity of ink, in cubic centimeters, per square meter of surface of the anilox roller. Theoretically, the ink transfer number should correspond to the total volume of the cells, in cubic centimeters per square meter of the anilox roller. Actually, the ink transferred is somewhat less since somewhat less ink is removed from the cells during printing than theoretically possible.
It has been found that, in operation, the surface changes due to wear of the ribs and walls of the cells which, in turn, changes the volume of the cells. The volume will decrease as the ribs or ridges between the cells are worn away by the engagement with the doctor blades, during printing. Thus, the ink transfer number changes. This is undesirable in printing operations resulting in loss of ink density.